HOMOLEPTIC ALKYNE-NICKEL(0) COMPLEXES - C OMBINATION OF NICKEL(0) CENTERS WITH ALKYNYLSILANES RN1SI(-C-C-R-2)(4-N) TO FORM ORGANONICKEL ANALOGS OF SILOXANES

(cod)(2) Ni reacts with Ph3Si-C=C-CMe3 to form the mixed complex (cad) Ni(alkyne) (1), (cdt)Ni and Ph3Si-C=C-CMe3 yield the homoleptic compou nd (alkyne)(2)Ni (2) (cod: cyclooca-1.5-diene, cdt: cyclododeca-1.5.9- triene). Both crystal structures were determined by X-ray diffraction analysis. In 2 the Ni(0) center is surrounded by the four carbon atoms of the alkynes yielding a distorted nickel-centered C-4 tetrahedron ( NiC4). Reaction of the alkynylsilanes Ph2Si(-C=C-R)(2) (R=CMe3, SiMe3) and of PhSi(-=C-CMe3)(2) with (cdt)Ni gives dimeric compounds of the type [(alkinylsilane)Ni(0)](2) (3-5), which have been characterized by X-ray diffraction determination. 3-5 show very similar structures in the solid state. Two silicon-centered C-4 tetrahedra (SiC4) are connec ted with two NiC4 tetrahedra by the four carbon atoms which are relate d to the two different kinds of tetrahedra. This structural principle can be compared with the structure of tetrasiloxanes. According to the temperature-dependent C-13 NMR spectra of 5 several conformers can be detected in solution.